Photo mask, exposure method using the same, and method of generating data

ABSTRACT

A photo mask formed with patterns to be transferred to a substrate using an exposure apparatus, the photo mask comprising a pattern row having three or more hole patterns surrounded by a shielding portion or a semitransparent film and arranged along one direction, and an assist pattern surrounded by the shielding portion or semitransparent film and having a longitudinal direction and a latitudinal direction, the assist pattern being located at a specified distance from the pattern row in a direction orthogonal to the one direction, the longitudinal direction of the assist pattern being substantially parallel with the one direction, the longitudinal length of the assist pattern being equivalent to or larger than the longitudinal length of the pattern row, the assist pattern being not transferred to the substrate.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority fromprior Japanese Patent Applications No. 2003-125576, filed Apr. 30, 2003;and No. 2004-115702, filed Apr. 9, 2004, the entire contents of both ofwhich are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a photo mask having an assist patternformed adjacent to a pattern, a method of manufacturing a semiconductordevice using the photo mask, and a method of generating data for thephoto mask.

2. Description of the Related Art

In the prior art, in forming fine hole patterns using a photo mask,resolution is improved by locating assist patterns with the same shapeas that of main patterns, around the main patterns (FIG. 1 in Jpn. Pat.Appln. KOKAI Publication No. 10-239827). However, it will be assumedthat a photo mask is projected and exposed which has, as a part of thewhole pattern, a pattern row of fine contiguous hole patterns 401 suchas those shown in FIG. 33. FIG. 34 shows the addition of assist patterns402 to the pattern row shown in FIG. 33. However, the mask pattern shownin FIG. 34 has an insufficient resolution for the hole patterns 401 andthus only a small lithography margin.

There is a technique to form an assist pattern adjacent to a patternhaving periodicity with respect to its adjacent patterns (Jpn. Pat.Appln. KOKAI Publication No. 7-140639). It will be assumed that theassist pattern is formed adjacent to a pattern not having periodicitywith respect to the adjacent patterns. That is, the assist pattern islocated adjacent to a rectangular pattern in its latitudinal direction.Also in this case, the rectangular pattern has an insufficientresolution and thus only a small lithography margin.

BRIEF SUMMARY OF THE INVENTION

According to an aspect of the present invention, there is provided aphoto mask formed with patterns to be transferred to a substrate usingan exposure apparatus, the photo mask being characterized by comprisinga pattern row having three or more hole patterns surrounded by ashielding portion or a semitransparent film and arranged along onedirection, and an assist pattern surrounded and formed by the shieldingportion or semitransparent film and having a longitudinal direction anda latitudinal direction, the assist pattern being located at a specifieddistance from the pattern row in a direction orthogonal to the onedirection, the longitudinal direction of the assist pattern beingsubstantially parallel with the one direction, the longitudinal lengthof the assist pattern being equivalent to or larger than thelongitudinal length of the pattern row, the assist pattern being nottransferred to the substrate.

According to an aspect of the present invention, there is provided amethod of manufacturing a semiconductor device, the method beingcharacterized by comprising providing an exposure apparatus whichtransfers patterns formed on a photo mask to a resist film on asemiconductor substrate, providing the photo mask having patterns to betransferred to the substrate, the photo mask comprising a pattern rowhaving three or more hole patterns surrounded by a shielding portion ora semitransparent film and arranged along one direction, and an assistpattern surrounded and formed by the shielding portion orsemitransparent film and having a longitudinal direction and alatitudinal direction, the assist pattern being located at a specifieddistance from the pattern row in a direction orthogonal to the onedirection, the longitudinal direction of the assist pattern beingsubstantially parallel with the one direction, the longitudinal lengthof the assist pattern being equivalent to or larger than thelongitudinal length of the pattern row, the assist pattern being nottransferred to the substrate, and transferring the patterns formed onthe photo mask to the resist film using the exposure apparatus.

According to an aspect of the present invention, there is provided amethod of generating design data for a photo mask formed with patternsto be transferred to a substrate using an exposure apparatus, the methodbeing characterized by comprising providing pattern data having apattern row in which three or more hole patterns are arranged in onedirection, executing a resizing process and a differentiating process onto generate an assist pattern, the longitudinal length of the assistpattern being equivalent to or larger than the length of the pattern rowin one direction, the longitudinal direction of the assist pattern beingsubstantially parallel with the one direction, the assist pattern beingnot transferred to the substrate; and merging the pattern data with theassist pattern to create the design data.

According to an aspect of the present invention, there is provided aphoto mask formed with patterns to be transferred to a substrate usingan exposure apparatus, the photo mask being characterized by comprisinga main pattern surrounded by a shielding portion or a semitransparentfilm and having a longitudinal direction and a latitudinal direction,the main pattern being located so as not to have periodicity withrespect to any patterns which are adjacent to the main pattern and whichare transferred to the substrate, and an assist pattern surrounded bythe shielding portion or semitransparent film, the assist pattern beinglocated close to one end of the main pattern in the longitudinaldirection, the width of the assist pattern in a direction parallel withthe latitudinal direction of the main pattern being larger than thelatitudinal width of the main pattern, the assist pattern being nottransferred to the substrate.

According to an aspect of the present invention, there is provided aphoto mask formed with patterns to be transferred to a substrate usingan exposure apparatus, the photo mask comprising: a pattern row in whicha plurality of line patterns each composed of a light shielding portionor a translucent film and having a longitudinal direction a latitudinaldirection orthogonal to the longitudinal direction are periodicallyarranged in the latitudinal direction; and an assist pattern composed ofthe light shielding portion or translucent film and placed near a lineend of the main patterns, the assist pattern having a length in thelatitudinal direction of the line patterns which is larger than thelength of the pattern row, the assist pattern not being transferred tothe substrate.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1 is a diagram schematically showing a circuit in a NAND type flashmemory according to a first embodiment;

FIG. 2 is a plan view showing the configuration of the flash memoryaccording to the first embodiment;

FIG. 3 is a sectional view showing the configuration of the flash memoryaccording to the first embodiment;

FIGS. 4A and 4B are a diagram schematically showing the configuration ofthe flash memory according to the first embodiment;

FIG. 5 is a graph showing the dependence of a focal depth and alongitudinal dimension on a gap d/length b;

FIGS. 6A and 6B are a diagram showing how diffracted light is generatedfrom dense patterns and formed into an image;

FIGS. 7A and 7B are a diagram illustrating the principle of improvementof the focal depth using grazing incidence illumination;

FIG. 8 is a diagram illustrating the principle of improvement of thefocal depth using grazing incidence illumination;

FIGS. 9A to 9F are a plan view showing the configurations of apertures(illumination condition);

FIG. 10 is a plan view showing the configuration of a photo mask usedfor simulation;

FIG. 11 is a graph showing the relationship between a Exposure toleranceand the focal depth;

FIGS. 12A and 12B are a diagram showing the configuration of a maskaccording to a second embodiment;

FIGS. 13A and 13B are a diagram showing the configuration of a maskaccording to a second embodiment;

FIGS. 14A to 14F are a diagram illustrating a method of generating maskdata according to a fourth embodiment;

FIGS. 15A to 15F are a diagram illustrating a method of generating maskdata according to a fifth embodiment;

FIG. 16 is a plan view showing the configuration of a phase shift maskformed with an assist pattern according to a sixth embodiment;

FIG. 17 is a plan view showing the configuration of a phase shift masknot formed with any assist patterns;

FIG. 18 is a graph showing the results of ED-Tree analysis of the phaseshift mask shown in FIG. 16;

FIG. 19 is a graph showing the results of ED-Tree analysis of the phaseshift mask shown in FIG. 17;

FIG. 20 is a graph showing the relationship between the focal depth at afocal tolerance of 8% and the length L of the assist pattern;

FIG. 21 is a graph showing a standardized light intensity on a substrateobtained if the phase shift mask shown in FIG. 16 is used;

FIG. 22 is a graph showing the standardized light intensity on thesubstrate obtained if the phase shift mask shown in FIG. 17 is used;

FIG. 23 is a graph showing the distribution of the light intensity ofexposure light on a substrate in the direction of a y axis, the exposurelight being transmitted through the phase shift mask shown in FIG. 16;

FIG. 24 is a graph showing the relationship between the ratio of a peakB to a peak A (B/A) and the assist pattern width W;

FIG. 25 is a graph showing the distribution of the light intensity ofexposure light on the substrate in the direction of an x axis, theexposure light being transmitted through the phase shift mask;

FIG. 26 is a graph showing the relationship between the ratio of a peakD to a peak C (D/C) and a distance d;

FIG. 27 is a plan view showing the configuration of a photo maskaccording to a seventh embodiment;

FIG. 28 is a flow chart showing the procedure of a method of generatingdesign data according to the seventh embodiment;

FIG. 29 is a diagram showing a line and space pattern;

FIG. 30 is a graph showing a normalized exposure light intensitydistribution on a resist film obtained if the L/S pattern is transferredto the resist film;

FIG. 31 is a graph showing a normalized exposure light intensitydistribution obtained if a pattern corresponding to design data istransferred to the resist film at an exposure light intensity β;

FIG. 32 is a chart showing the procedure of a method of manufacturing asemiconductor device according to a eighth embodiment;

FIG. 33 is a plan view showing a pattern row having a plurality of holepatterns arranged along one direction; and

FIG. 34 is a diagram showing a pattern having assist patterns added tothe pattern row shown in FIG. 33.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the present invention will be described below withreference to the drawings. Naturally enough, the present invention isnot limited by the embodiments shown below.

(First Embodiment)

In the present embodiment, description will be given of an example inwhich the present invention is applied to a case where a photo mask fora bit line contact (CB) layer of a NAND flash memory is projected andexposed, the photo mask having, as a part of the whole pattern, holesarranged contiguously in one-dimensional direction.

FIG. 1 schematically shows a circuit in the NAND type flash memory.

As shown in FIG. 1, each NAND type flash memory is composed ofnonvolatile semiconductor memory cells M are connected together inseries. One end of the NAND type flash memory is connected to a bit lineBL via a section transistor S connected to a selection gate line SG (SG1or SG1′). Each memory cell is connected to a control gate line (CG1 toCG4, CG1′). The other end (not shown) of the flash memory is connectedto a common source line via a selection transistor connected to theselection gate line.

FIG. 2 is a plan view of the NAND type flash memory. FIG. 3 shows across section of the flash memory taken along line II-II′ in FIG. 2.

As shown in FIGS. 2 and 3, a p-type well 102 is formed on an n-type Si102. An n-type diffusion layer 103 is formed in parts of the p-type well102. The n-type diffusion layer 103 constitutes a source and a drain ofthe non-volatile memory cell M. A tunnel insulating film 104 is formedon a channel region. A floating gate 105 is formed on the tunnelinsulating film 104. An inter-gate insulating film 106 is formed on thefloating gate 105. A control gate 107 is formed on the inter-gateinsulating film 106. In the selection transistor S, the inter-gateinsulating film 106 is partly removed. Furthermore, the floating gate105 and the control gate 107 are electrically connected together toconstitute the selection gate SG.

An inter-layer insulating film 109 is formed on the Si substrate 101. Acontact hole 110 is formed in the inter-layer insulating film 109 so asto connect to the n-type diffusion layer 103 located between the twoselection transistors S. A bit line contact 111 is formed in the bitline contact hole 110 and on the inter-layer insulating film. A secondinter-layer insulating film 112 is formed on the bit line contact 111. Avia plug 113 is formed in a hole formed in the second inter-layerinsulating film 112. A bit line 114 is formed on the second inter-layerinsulating film 112 so as to connect to the via plug 113.

As shown in FIG. 2, the longitudinal dimension of the bit line plug holesignificantly affects a chip size. The chip size and thus chip costsdecrease consistently with the longitudinal dimension of the bit lineplug hole. It is thus important to improve the resolution of the bitline contact, provide dimensional controllability, and reduce thelongitudinal dimension.

In the present embodiment, a mask is designed so that the bit linecontact hole has a pitch of 145 nm and that the short side of one holeis 72.5 mm. FIGS. 4A and 4B are a diagram showing the configuration of amask according to a first embodiment of the present invention. FIG. 4Ais a plan view of the mask, and FIG. 4B is a sectional view of the masktaken along line IV-IV′ in FIG. 4A.

As shown in FIG. 4A, three or more hole patterns 201 are arranged alongone direction. Each of the hole patterns 201 is a rectangular of sizea=50 nm×b=350 nm. An assist pattern 202 (202 a and 202 b) of width W 50nm is formed at a distance d of 300 nm from the hole patterns 201 in adirection orthogonal to the direction in which the hole patters 201 arearranged (the one direction). The assist pattern 202 is not transferredto the substrate when it is exposed using an exposure apparatus in whichthe mask is mounted. The assist pattern has a length equivalent to orlarger than that of the hole pattern row in the one direction. The longside of the assist pattern (in its longitudinal direction) issubstantially parallel with the arrangement direction. As shown in FIG.4B, the hole pattern 201 and the assist patterns 202 a and 202 b aresurrounded by a semitransparent film 211 formed on a transparentsubstrate 210.

If the assist pattern 202 has a width W larger than 0.3×λ/numericalaperture NA (in the present embodiment, 68 nm), then it is undesirablylikely to be transferred.

As shown in FIG. 5, if a gap d is less than 0.3×b the length b of thehole pattern, then it is larger than a target dimension (0.15 μm). Thisis not preferable. Accordingly, the gap d is at least 0.3×b with respectto the length b. If the gap d is larger than 1.5×b, a focal depth mayundesirably be excessively short. Moreover, the relationship between thegap d and the length b is preferably 0.5×b≦d≦1.0×b, which results in asufficiently large focal depth. FIG. 5 is a graph showing the dependenceof the focal depth and longitudinal dimension on the gap d/length b.

The suitable illumination depends on whether the patterns are sparselyor densely arranged. For the bit line contact hole, the patterns aredensely arranged in the short side direction but are sparsely arrangedin the long side direction. In a photo mask having the assist patterns402 shown in FIG. 17, the patterns are dense in the arrangementdirection and in the direction perpendicular to the arrangementdirection but are sparse in oblique directions.

In the mask according to the present embodiment, the assist patterns,which are not transferred, are arranged adjacent to each other in thelongitudinal direction. Consequently, the patterns are also denselyarranged in the oblique directions. As a result, the mask is suitablefor an illumination condition for the case in which the patterns aredensely arranged. This improves resolution and the focal depth.

The illumination condition for the case in which the patterns aredensely arranged is grazing incidence illumination. With reference toFIGS. 6 to 8, description will be given of the reason why the grazingincidence is suitable for dense patterns. FIGS. 6A and 6B are a diagramshowing how diffracted light is generated from the dense patterns andformed into an image. FIG. 6A shows a case of vertical illumination.FIG. 6B shows a case of grazing incidence illumination. As shown in FIG.6A, with the vertical illumination, ±1st-order lights have an anglelarger than the NA of a projection lens. Only 0th-order light reaches awafer. As shown in FIG. 6B, with the grazing incidence illumination, animage can be formed on the wafer provided that 0th-order light and1st-order light pass through the projection optical system.Consequently, the grazing incidence illumination enables a limitedresolution to be improved.

FIGS. 7A and 7B are a diagram illustrating the principle of improvementof the focal depth using the grazing incidence illumination. FIG. 7Ashows how the vertical illumination is diffracted and formed into animage. FIG. 7B shows how the grazing incidence illumination isdiffracted and formed into an image. The pitch of the mask is defined asP, and a wavelength is defined as λ. Furthermore, the angle between the0th-order light and 1st-order light passing through the mask is definedas θ, and the numerical aperture of the lens is defined as NA. Then therelationship P=λ/sin θ=λ/NA. As shown in FIGS. 7A and 7B, if theillumination is changed to the grazing incidence with the pitch of themask remaining unchanged, then the focal depth is improved compared tothe vertical illumination. This is because the angle between 1st-orderdiffracted light and 0th-order diffracted light is small.

FIG. 8 is a diagram illustrating the principle of improvement of theresolution using the grazing incidence illumination. As shown in FIG. 8,the value θ and the resolution increase consistently with the pitch.

Simulation was executed to determine a resist pattern formed if the maskin which the continuous assist patterns are formed is used to exposeresist. Then, optimum exposure conditions were determined. In thesimulation, a spatial image was calculated for the mask pattern. Then,the effect of a resist process was loaded using a convolution integralof a Gaussian function (σ=ΔL), to calculate the resist pattern. Theeffect of the resist process was predetermined by fitting simulationresults to experimental results. ΔL=45 nm.

The wavelength λ of an illuminating light source was set at 193 nm.Comparative examinations were made by varying the numerical aperture NAand the aperture of the illuminating optical system (illuminationconditions). FIGS. 9A to 9F show the configuration of the aperture usedfor the simulation. FIG. 9A shows normal illumination and FIG. 9B showszone illumination. FIG. 9C shows two-pole illumination and FIG. 9D showsfour-pole illumination. FIG. 9E shows two-blank-sector illumination andFIG. 9F shows four-blank-sector illumination. Furthermore, the numericalaperture was set at 0.68, 0.78, or 0.85. For the two-pole illumination,the diameters of two openings formed in the aperture may be varieddepending on the conditions. Likewise, for the four-pole illumination,the diameters of openings formed in the aperture may be varied dependingon the conditions. Furthermore, although the figures show four-rotationsymmetry, two-rotation symmetry may be used.

The results of the simulation indicated that the optimum numericalaperture was 0.85 and that the two-blank-sector illumination was optimumfor the aperture of the illumination system. The parameters for thetwo-blank-sector illumination were set as follows: σ=0.9, Innerσ=0.6,and θoal=30 [deg]. The openings were arranged so that the mask would beilluminated obliquely with respect to the short side direction of thearrangement direction. This configuration improved the resolution of thebit line contact hole. It was also possible to form contiguous holepatterns having a pitch of 145 nm and a long side dimension of 150 nm.In this connection, varied illumination methods other than thetwo-blank-sector illumination have large margins. Accordingly, othervaried illumination methods may be used.

Lithography simulation was executed by varying the width of an assistpattern 203 step by step until it is connected to its adjacent assistpattern 203. The patterns other than the assist patterns 203, that is,the patterns 201 have dimensions similar to those shown in FIGS. 4A and4B.

The illumination condition was the two-blank-sector illumination and thenumerical aperture was 0.85. The results of the simulation are shown inFIG. 11. Furthermore, Table 1 shows a summary of the results of thesimulation. Table 1 shows the focal depth observed when a exposuretolerance is 8%. TABLE 1 Assist pattern width [nm] Focal SRAF a depthDOF [nm]  0 169 (No assist)  50 180 100 191 145 201 (Continuous)

This indicates that the assist patterns according to the presentembodiment provide the largest lithography margin.

(Second Embodiment)

FIG. 12A is a plan view of the mask. FIG. 12B is a sectional view of themask taken along line XII-XII′ in FIG. 12A. This mask is used to formbit line contact holes of a NAND type flash memory.

FIGS. 12A and 12B are a diagram showing the configuration of a maskaccording to a second embodiment of the present invention. There or morehole patterns 201 are arranged along one direction. Each of the holepatterns 201 is a rectangular of size a=40 nm×b=200 nm. A second assistpattern 222 (222 a and 222 b) of width W 50 nm is formed at a distance dof 300 nm from the hole patterns 201 in a direction orthogonal to thedirection in which the hole patters 201 are arranged (the onedirection). The second assist pattern 222 is not transferred to thesubstrate when it is exposed using the exposure apparatus in which themask is mounted. At the second assist pattern, the transparent substrate210 is dug. As a result, there is a phase difference of 180 0 betweenlight transmitted through the second assist pattern 222 and lighttransmitted through the hole pattern 201. A first assist pattern 223(223 a and 223 b) of width W 50 nm is formed at a distance d of 300 nmfrom the second assist pattern 222 in the direction orthogonal to thedirection in which the hole patters 201 are arranged (the onedirection). The first assist pattern 223 is not transferred to thesubstrate when it is exposed using the exposure apparatus in which themask is mounted. Light transmitted through the first assist pattern 223and light transmitted through the hole pattern 201 are in phase.

Exposure was carried under the same illumination conditions as those inthe first embodiment. Then, it was able to form contiguous hole patternshaving a pitch of 145 nm and a long side dimension of 130 nm.

In addition, although the Levenson type photo mask was shown in FIGS.12A and 12B, a half-tone type photo mask shown in FIGS. 13A and 13B maybe used to form bit line contact holes of a NAND type flash memory. FIG.13A is a plan view of the mask. FIG. 13B is a sectional view of the masktaken along line XII-XII′ in FIG. 13A. In FIG. 13B, a notation 213 is asemitransparent film.

(Third Embodiment)

In the present embodiment, the dimensions of each of the photo masksshown in FIGS. 4 and 12 were optimized to compare their long sidedimensions with each other. Table shows the dimensions of each of theoptimized photo masks. TABLE 2 Assist pattern shape a b W/W1 d/d1 W2 d2None 56 370 — — — — Isolated 60 300 50  50 — — assist pattern Continuous50 350 50 300 — — assist pattern (one) Continuous 40 200 50 200 50 50assist pattern (two)

Simulation was executed under illumination conditions were similar tothose in the first embodiment to determine the long side dimensions.Table 3 shows the long side dimensions of the hole formed at an exposuretolerance of 8% and a focal depth of 0.2 μm. TABLE 3 Long side dimensionAssist pattern shape [nm] None 160 Isolated assist pattern 157Continuous assist 150 pattern (one) Continuous assist 133 pattern (two)

Table 3 indicates that the long side dimension can be reduced using thecontinuous assist pattern, particularly the two continuous assistpatterns.

(Fourth Embodiments)

In the present embodiment, description will be given of a method ofgenerating data on a mask having the above continuous assist pattern.FIGS. 14A to 14F are a diagram illustrating a method of generating dataaccording to a fourth embodiment of the present invention.

First, as shown in FIG. 14A, design data is provided which indicatesthat there is a spacing S between adjacent hole patterns 301 and thatthree or more hole pattern data are arranged in one direction. Then, asshown in FIG. 14B, a resizing process is executed to extend each holepattern 301 by an amount S/2 rightward and leftward in an x direction.Thus, the adjacent patterns are joined together to create a pattern 302.Then, as shown in FIG. 14C, a resizing process is executed to extend thepattern 302 by an amount d (the distance between the main pattern andassist pattern)+W (the width of the assist pattern) upward and downwardin a y direction to create a pattern 303. Then, as shown in FIG. 14D, aresizing process is executed to shrink the pattern 303 upward anddownward in the y direction to generate a pattern 304. Then, as shown inFIG. 14E, differential patterns 305 a and 305 b between the pattern 303,shown in FIG. 14C, and the pattern 304, shown in FIG. 14D, areextracted. As shown in FIG. 14F, the pattern 301, shown in FIG. 14A, ismerged with the patterns 305 a and 305 b, shown in FIG. 14E. The aboveprocess enables the designing of a hole pattern having a continuousassist pattern.

(Fifth Embodiment)

In the present embodiment, description will be given of a method ofgenerating data on a mask having a continuous assist pattern. FIGS. 15Ato 15F are a diagram illustrating a method of generating data accordingto a fifth embodiment of the present invention.

First, as shown in FIG. 15A, design data is provided which indicatesthat there is a spacing S between adjacent hole patterns and that threeor more hole patterns (width a) 301 are arranged in one direction. Then,as shown in FIG. 15B, a resizing process is executed to extend thepatterns 301 by an amount d (the distance between the main pattern andassist pattern)+W (the width of the assist pattern) upward and downwardin the y direction to generate patterns 312. Then, as shown in FIG. 15C,a resizing process is executed to shrink the patterns 312 upward anddownward in the y direction to generate patterns 313. Then, as shown inFIG. 15D, a differential pattern 314 between each pattern 312, shown inFIG. 15B, and the corresponding pattern 313, shown in FIG. 15C, isextracted. Then, as shown in FIG. 15E, a resizing process is executed toextend each pattern by an amount S/2 rightward and leftward in the xdirection to generate patterns 315 a and 315 b. As shown in FIG. 15F,the pattern 301, shown in FIG. 15A, is merged with the patterns 315 aand 315 b, shown in FIG. 15E. The above process enables the designing ofa hole pattern having a continuous assist pattern.

(Sixth Embodiment)

In view of the above described problems, the inventor invented a methodof arranging assist patterns in a phase shift mask with respect to holepatterns not having periodicity

Description will be given of a phase shift mask according to embodimentsof the present invention and the formation of hole patterns using thephase shift mask.

FIG. 16 is a plan view showing the configuration of a phase shift maskaccording to a sixth embodiment of the present invention. As shown inFIG. 16, a main pattern 501 and an assist pattern 502 (502 a and 502 b)are surrounded by a semitransparent film 511. The semitransparent film511 is formed on a transparent substrate (not shown). Thesemitransparent film has a light transmittance of 6%. Light transmittedthrough the semitransparent film is 180 0 out of phase compared to lighttransmitted through the hole pattern 501 and assist patterns 502 a and502 b. The phase shift mask is mounted in an exposure apparatus with anexposure wavelength λ and a numerical aperture NA. With this phase shiftmask, the patterns are preferably transferred to the substrate usinggrazing incidence illumination.

The main pattern 501 is located so as not have periodicity with respectto any patterns that lie adjacent to the main pattern 501 and that aretransferred to the substrate if it is exposed using the exposureapparatus in which the phase shift mast is mounted. The main pattern 501is shaped like a rectangle with rounded corners. The main pattern 501has a latitudinal direction in the x direction and a longitudinaldirection in the y direction.

The assist patterns 502 a and 502 b are arranged close to one end of themain pattern in the longitudinal direction. The assist pattern 502 isnot transferred to the substrate if it is exposed using the exposureapparatus in which the phase shift mast is mounted. The length L of theassist pattern 502 in the x direction is sufficiently larger than thewidth of the main pattern 501 in the x direction.

If the with of the assist pattern 502 in the y direction is larger than0.27× the exposure wavelength λ/the numerical aperture NA, the assistpattern is undesirably likely to be transferred. The phase shift maskwith the assist pattern was subjected to ED-Tree analysis. Furthermore,ED tree analysis was performed on a phase shift mask in which only themain pattern 501 is formed as shown in FIG. 17. FIGS. 17 and 18 show theresults of the ED-Tree analysis. FIG. 18 shows the results of theED-Tree analysis of the phase shift mask in which the assist pattern isformed as shown in FIG. 16. FIG. 19 shows the results of the ED-Treeanalysis of the phase shift mask in which the assist pattern is notformed as shown in FIG. 17. In FIGS. 18 and 19, L-20%, L0%, and L+20%denote lines with which the length of the transferred main pattern 501in the y direction is −20%, 0%, and +20% of a designed dimension. InFIGS. 18 and 19, L-10%, L0%, and L+10% denote lines with which thelength of the transferred main pattern 501 in the x direction is −10%,0%, and +10% of a designed dimension.

As shown in FIGS. 18 and 19, the presence of the assist margin reducesvariations in dimensions when the side of the hole perpendicular to theassist pattern is defocused. This serves to improve the lithographymargin.

The lithography margin was evaluated using the length L of the assistpattern 502 in the x direction as a parameter. The lithography margin isthe focal depth observed at a focal tolerance of 8%. FIG. 20 is a graphshowing the results of evaluation of the lithography margin. As shown inFIG. 20, when the assist pattern 502 has a length of about 1,000 nm, thelithography margin (focal depth) tends to be saturated.

With the phase shift mask with the assist pattern 502 and the phaseshift mask without the assist pattern 502, the distribution of a lightintensity on the substrate was simulated. FIG. 21 shows a standardizedlight intensity on the substrate obtained if the phase shift mask withthe assist pattern 502 is used. FIG. 22 shows the standardized lightintensity on the substrate obtained if the phase shift mask without theassist pattern 502 is used. The standardized light intensity iscomparable between the phase shift mask with the assist pattern 502 andthe phase shift mask without the assist pattern 502.

The light intensity on the substrate was simulated by transferring thepattern formed on the phase shift mask was transferred. FIG. 23 showsthe distribution of the light intensity in the direction of the y axis.FIG. 23 shows the distribution of the light intensity of exposure lighton the substrate in the direction of the y axis, the exposure lightbeing transmitted through the phase shift mask. In FIG. 23, a peak Bresults from the assist pattern. When the light intensity of the peak Bis high, the pattern is transferred to the wafer. Accordingly, theassist pattern width W must be optimized.

Simulation was executed using the assist pattern width W as a parameterto determine the ratio of the peak B to the peak A (B/A). Exposureconditions included an exposure wavelength of 193 nm and a numericalaperture NA of 0.85. FIG. 24 is a graph showing the relationship betweenthe ratio of the peak B to the peak A (B/A) and the assist pattern widthW. In this case, the assist pattern width W was 50 nm when thestandardized exposure intensity was comparable to that obtained withoutthe assist pattern.

The light intensity on the substrate was simulated by transferring thepattern formed on the phase shift mask was transferred. FIG. 25 showsthe distribution of the light intensity in the direction of the x axis.FIG. 25 shows the distribution of the light intensity of exposure lighton the substrate in the direction of the x axis, the exposure lightbeing transmitted through the phase shift mask. The distribution of thelight intensity has peaks C and D. The peak C results from the mainpattern. The peak D is expected to result from the assist pattern.Simulation was executed using the distance d between the main patternand the assist pattern to determine the ratio of the peak D to the peakC (D/C). FIG. 26 is a graph showing the relationship between the ratioof the peak D to the peak C (D/C) and the distance d. As shown in FIG.26, the ratio (D/C) varies with the distance. This indicates that thedistance d must be optimized. In the present embodiment, the distance dbetween the assist pattern and the main pattern was 100 nm. However,Distance d is not limited to 100 nm and is at least 50 nm.

(Seventh Embodiment)

FIG. 27 is a plan view showing the configuration of a photo maskaccording to a seventh embodiment of the present invention. Thedimensions of the photo mask shown in the present embodiment and each ofthe subsequent embodiments exhibit their values obtained when the photomask is transferred to a substrate.

As shown in FIG. 27, a plurality of line patterns 601 are periodicallyarranged in the x direction. The plurality of line patterns 601constitute an L/S pattern. Assist patterns 602 a and 602 b are arrangedadjacent to one end of the line patterns 601 in the y direction. Theassist patterns 602 a and 602 b have a length in the x direction whichis equal to or larger than the length of the L/S pattern in the xdirection. Even when used for the exposure apparatus used, the assistpatterns 602 a and 602 b are not transferred to the substrate. It isundesirable that in connection with the numerical aperture NA, the widthof the assist patterns 602 a and 602 b in the y direction is larger than0.26×λ/NA (in the present example, 59 nm). This is because thisdimension makes the assist patterns 602 a and 602 b more likely to betransferred to the resist on the substrate. The hole patterns 601 andthe assist patterns 602 a and 602 b are each formed of a light shieldingfilm formed on a transparent film. The hole patterns 601 and the assistpatterns 602 a and 602 b may each be formed of a translucent film formedon a transparent film.

If the L/S pattern L and the assist patterns 602 a and 602 b aretransferred to the resist film on the substrate using the exposureapparatus and are then developed, then it is possible to reduce themagnitude of shortening and thinning that may occur at the end of theline patterns formed. As a result, when a resist pattern is formed, themagnitude of a possible falling of the resist pattern can be reduced.

Moreover, although the assist pattern located close to one end of theline pattern 601 in the y direction, the assist pattern may locatedclose to other end of the line pattern 601 in the y direction. Moreover,although two assist patterns 602 a and 602 b are arranged, only oneassist pattern may be formed and three or more assist patterns may bearranged again. Moreover, distance d of the line pattern 601 and assistpattern 602 a is preferably 0.5×b≦d≦1.0×b larger than 50 nm.

Now, description will be given of a method of generating design datacontaining the assist patterns, from design data containing the L/Spattern. FIG. 28 is a flow chart showing the procedure of a method ofgenerating design data according to the seventh embodiment of thepresent invention.

First, first design data is provided which has the L/S pattern LScomposed of the plurality of line patterns 601 shown in FIG. 29 (stepST11). In the pattern corresponding to the first design data, no assistpatterns are arranged adjacent to the L/S pattern. Then, lithographysimulation is executed to determine a normalized exposure lightintensity distribution on a resist film obtained if the L/S pattern istransferred to the resist film (step ST12). FIG. 30 shows the determinednormalized exposure light intensity distribution. FIG. 30 shows thenormalized exposure light intensity distribution in the x direction.

An exposure light intensity a with which target pattern dimensions areobtained is determined from the normalized exposure light intensitydistribution (step ST13). Further, an exposure light intensity β that is20% higher than the exposure light intensity α is determined (stepST13). The exposure light intensity β corresponds to the upper limitvalue of an exposure amount margin.

Now, a plurality of design data (a group of design data) are provided inwhich the assist patterns 602 are arranged adjacent to the L/S patternas shown in FIG. 27 (step ST15). The width W of the assist patterns inthe x direction and the distance d between the L/S pattern and theassist patterns vary among the plurality of design data.

Lithography simulation is executed to determine a normalized exposurelight intensity distribution on a resist film obtained if the patternscorresponding to each data are transferred to the resist film with theexposure light intensity β (step ST16). FIG. 31 shows the determinednormalized exposure light intensity distribution. FIG. 31 shows thenormalized exposure light intensity distribution in the y direction. InFIG. 31, a peak Pa corresponds to the assist pattern 602 a. A peak Pbcorresponds to the assist pattern 602 b.

One of the design data is selected on the basis of the plurality ofexposure light intensity distributions obtained (step ST17); with thisdesign data, if the patterns are transferred with the exposure lightintensity β, the assist patterns are not transferred to the resist. Inthe present embodiment, the following condition is set: the assistpatterns are not designed if the peaks Pa and Pb exhibit the exposurelight intensity β or higher.

The above process provides a design that allows the assist patterns tobe arranged near the line end of the line patters, the main patterns.

(Seventh Embodiment)

Description will be given of a method of manufacturing a semiconductordevice using the photo mask described in the first to third and sixthembodiments. FIG. 32 is a flow chart showing the procedure of a methodof manufacturing a semiconductor device according to a seventhembodiment.

Design data is provided which relates to a photo mask having an assistpattern dimensioned in association with the exposure apparatus used totransfer the pattern. A photo mask is produced on the basis of thedesign data (step ST101). The photo mask is stored in a exposureapparatus (step ST102).

A semiconductor substrate in which, for example, an inter-layerinsulating film and the like are formed. A positive resist film iscoated and formed on the semiconductor substrate (step ST103). Thesemiconductor substrate is stored in the exposure apparatus. To form alatent image on the resist film, the exposure apparatus is used totransfer the pattern formed on the photo mask to the resist film (stepST104). The resist film is developed (step ST105). The inter-layerinsulating film is etched using the developed resist film as a mask(step ST106). Subsequently, further processing is executed tomanufacture a semiconductor device.

Additional advantages and modifications will readily occur to thoseskilled in the art. Therefore, the invention in its broader aspects isnot limited to the specific details and representative embodiments shownand described herein. Accordingly, various modifications may be madewithout departing from the spirit or scope of the general inventiveconcept as defined by the appended claims and their equivalents.

1. A photo mask formed with patterns to be transferred to a substrateusing an exposure apparatus, the photo mask comprising: a pattern rowhaving three or more hole patterns surrounded by a shielding portion ora semitransparent film and arranged along one direction; and an assistpattern surrounded by the shielding portion or semitransparent film andhaving a longitudinal direction and a latitudinal direction, the assistpattern being located at a specified distance from the pattern row in adirection orthogonal to the one direction, the longitudinal direction ofthe assist pattern being substantially parallel with the one direction,the longitudinal length of the assist pattern being equivalent to orlarger than the longitudinal length of the pattern row, the assistpattern being not transferred to the substrate.
 2. The photo maskaccording to claim 1, wherein lights transmitted through the respectivehole patterns are in phase, the assist pattern includes a first assistpattern for which transmitted light is in phase with the lightstransmitted through the hole patterns and a second assist pattern whichis located between the first assist pattern and the hole pattern and forwhich transmitted light is 180 0 out of phase with the lightstransmitted through the hole patterns.
 3. The photo mask according toclaim 1, wherein the exposure apparatus has an exposure wavelength λ anda numerical aperture NA, and the width of the assist pattern in thedirection orthogonal to the one direction is at most 0.3×λ/NA.
 4. Thephoto mask according to claim 1, wherein a side of the hole patternwhich is perpendicular to the one direction of the hole pattern has alength b, and a distance d between the hole pattern and the assistpattern is at most 0.3×b.
 5. A method of manufacturing a semiconductordevice, the method comprising: providing an exposure apparatus whichtransfers patterns formed on a photo mask to a resist film on asemiconductor substrate; providing the photo mask comprising a patternrow having three or more hole patterns surrounded by a shielding portionor a semitransparent film and arranged along one direction, and anassist pattern surrounded by the shielding portion or semitransparentfilm and having a longitudinal direction and a latitudinal direction,the assist pattern being located at a specified distance from thepattern row in a direction orthogonal to the one direction, thelongitudinal direction of the assist pattern being substantiallyparallel with the one direction, the longitudinal length of the assistpattern being equivalent to or larger than the longitudinal length ofthe pattern row, the assist pattern being not transferred to thesubstrate; and transferring the patterns formed on the photo mask to theresist film using the exposure apparatus.
 6. The method of manufacturinga semiconductor device according to claim 5, wherein the transferemploys an illumination method with which illumination light is incidenton the photo mask obliquely with respect to the one direction.
 7. Themethod of manufacturing a semiconductor device according to claim 5,wherein lights transmitted through the respective hole patterns are inphase, the assist pattern includes a first assist pattern for whichtransmitted light is in phase with the lights transmitted through thehole patterns and a second assist pattern which is located between thefirst assist pattern and the hole pattern and for which transmittedlight is 180 0 out of phase with the lights transmitted through the holepatterns.
 8. The method of manufacturing a semiconductor deviceaccording to claim 5, wherein the exposure apparatus has an exposurewavelength λ, a projection lens of the exposure apparatus has anumerical aperture NA, and the width of the assist pattern is at most0.3×λ/NA.
 9. The method of manufacturing a semiconductor deviceaccording to claim 5, wherein a side of the hole pattern which isperpendicular to the one direction of the hole pattern has a length b,and a distance d between the hole pattern and the assist pattern is atmost 0.3×b≦d.
 10. The method of manufacturing a semiconductor deviceaccording to claim 5, wherein the hole pattern is used to form bit linecontact holes of a NAND type flash memory.
 11. A method of generatingdesign data for a photo mask formed with patterns to be transferred to asubstrate using an exposure apparatus, the method comprising: providingpattern data having a pattern row in which three or more hole patternsare arranged in one direction; executing a resizing process and adifferentiating process on to generate an assist pattern, thelongitudinal length of the assist pattern being equivalent to or largerthan the length of the pattern row in one direction, the longitudinaldirection of the assist pattern being substantially parallel with theone direction, the assist pattern being not transferred to thesubstrate; and merging the pattern data with the assist pattern tocreate the design data.
 12. The method of generating data according toclaim 11, wherein the exposure apparatus has an exposure wavelength λ, aprojection lens of the exposure apparatus has a numerical aperture NA,and the width of the assist pattern is at most 0.3×λ/NA.
 13. The methodof generating data according to claim 11, wherein a distance d betweenthe hole pattern and the assist pattern and a side b of the hole patternwhich is perpendicular to the one direction of the hole pattern has arelationship 0.3×b≦d.
 14. A photo mask formed with patterns to betransferred to a substrate using an exposure apparatus, the photo maskcomprising: a main pattern surrounded by a shielding portion or asemitransparent film and having a longitudinal direction and alatitudinal direction, the main pattern being located so as not to haveperiodicity with respect to any patterns which are adjacent to the mainpattern and which are transferred to the substrate; and an assistpattern surrounded by the shielding portion or semitransparent film, theassist pattern being located close to one end of the main pattern in thelongitudinal direction, the width of the assist pattern in a directionparallel with the latitudinal direction of the main pattern being largerthan the latitudinal width of the main pattern, the assist pattern beingnot transferred to the substrate.
 15. The photo mask according to claim14, wherein the exposure apparatus has an exposure wavelength λ and anumerical aperture NA, and the width of the assist pattern is at most0.27×λ/NA.
 16. The photo mask according to claim 14, wherein a distancebetween the main pattern and the assist pattern is at least 50 nm on thesubstrate.
 17. A photo mask formed with patterns to be transferred to asubstrate using an exposure apparatus, the photo mask comprising: apattern row in which a plurality of line patterns each composed of alight shielding portion or a translucent film and having a longitudinaldirection a latitudinal direction orthogonal to the longitudinaldirection are periodically arranged in the latitudinal direction; and anassist pattern composed of the light shielding portion or translucentfilm and placed near a line end of the main patterns, the assist patternhaving a length in the latitudinal direction of the line patterns whichis larger than the length of the pattern row, the assist pattern notbeing transferred to the substrate.
 18. The method of generating dataaccording to claim 11, wherein the exposure apparatus has an exposurelight wavelength λ and a projection lens of the exposure apparatus has anumerical aperture NA, and the width W of the assist pattern in thelongitudinal direction of the line patterns is 0.27×λ/NA in terms ofdimensions on the substrate.
 19. The photo mask according to claim 17,wherein a distance between the main pattern and the assist pattern is atleast 50 nm on the substrate.
 20. A method of manufacturing asemiconductor device, the method comprising: providing an exposureapparatus which transfers patterns formed on a photo mask to a positiveresist film on a semiconductor substrate, the exposure apparatus isgrazing incidence illumination; providing the photo mask comprising amain pattern surrounded by a shielding portion or a semitransparent filmand having a longitudinal direction and a latitudinal direction, themain pattern being located so as not to have periodicity with respect toany patterns which are adjacent to the main pattern and which aretransferred to the substrate; and an assist pattern surrounded by theshielding portion or semitransparent film, the assist pattern beinglocated close to one end of the main pattern in the longitudinaldirection, the width of the assist pattern in a direction parallel withthe latitudinal direction of the main pattern being larger than thelatitudinal width of the main pattern, the assist pattern being nottransferred to the substrate; and transferring the patterns formed onthe photo mask to the positive resist film using the exposure apparatus.21. A method of manufacturing a semiconductor device, the methodcomprising: providing an exposure apparatus which transfers patternsformed on a photo mask to a positive resist film on a semiconductorsubstrate, the exposure apparatus using grazing-incidence illumination;providing the photo mask, the photo mask comprising a pattern row inwhich a plurality of line patterns each composed of a light shieldingportion or a translucent film and having a longitudinal direction alatitudinal direction orthogonal to the longitudinal direction areperiodically arranged in the latitudinal direction, and an assistpattern composed of the light shielding portion or translucent film andplaced near a line end of the main patterns, the assist pattern having alength in the latitudinal direction of the line patterns which is largerthan the length of the pattern row, the assist pattern not beingtransferred to the substrate; and transferring the patterns formed onthe photo mask to the positive resist film using the exposure apparatus.